1. Field of the Invention
The present invention relates to a passive coherent location (xe2x80x9cPCLxe2x80x9d) radar system and method, and more particularly, to a system and method for mitigating co-channel interference of received signals for PCL radar applications.
2. Discussion of the Related Art
PCL radar systems may be represented by a multistatic radar system. A multistatic radar system has many receivers that are separated from one or more transmitters. The radiated signal from a transmitter arrives at a receiver via two separate paths. One path may be a direct path from the transmitter to the receiver, and the other path may be a target path that includes an indirect path from the transmitter to a target to the receiver. Measurements may include a total path length, or transit time, of the target path signal, the angle of arrival of the target path signal, and the frequency of the direct and target path signals. A difference in frequency may be detected if the target is in motion according to a doppler effect.
Knowledge of the transmitted signal is desirable at the receiver if information is to be extracted from the target path signal. The transmitted frequency is desired to determine the doppler frequency shift. A time or phase reference also is desired if the total scattered path length is to be determined. The frequency reference may be obtained from the direct signal. The time reference also may be obtained from the direct signal provided the distance between the transmitter and the receiver is known.
Multistatic radar may be capable of determining the presence of a target within the coverage of the radar, the location of the target position, and a velocity component, or doppler, relative to the radar. The process of locating the target position may include a measurement of a distance and the angle of arrival. The measurement of distance relative to the receiving site may desire both the angle of arrival at the receiving site and the distance between transmitter and receiver. If the direct signal is available, it may be used as a reference signal to extract the doppler frequency shift.
In PCL radar systems, transmitters may be known as illuminators. Illuminators may be wideband sources of opportunities that include commercial frequency modulated (xe2x80x9cFMxe2x80x9d) broadcast transmitters and/or repeaters, commercial high-definition television (xe2x80x9cHDTVxe2x80x9d) broadcast transmitters and/or repeaters, and the like. Techniques for wideband signal pre-detection processing and co-channel interference mitigation exist. Known approaches include an array of antennas used to receive the source of opportunity to be exploited, such as the primary illuminator, and any other co-channel signals present in the environment.
Co-channel signals may include multipath images of the illuminator signal, delay and Doppler-shifted reflections of the illuminator from targets in the region under surveillance and other distant broadcast sources at the same operating frequency as the primary illuminator. Targets may include aircraft, space launch vehicles and the like. The intent of the co-channel mitigation techniques is to eliminate the undesirable sources from the received antenna outputs, such as the strong direct path and multipath components of the exploited illuminator, while leaving the reflected signals from targets of interest unattenuated. Thus, it is desirable to improve co-channel mitigation techniques to better identify and track targets, and to determine target location, range and velocity.
Accordingly, embodiments of the present invention are directed to a PCL application and method for signal processing within the PCL application.
Thus, the present invention is directed to a system and method for mitigating co-channel interference. According to an embodiment, a method for mitigating co-channel interference in co-channel signals in a bistatic radar is disclosed. The method includes identifying a primary illuminator signal from a primary illuminator. The primary illuminator signal comprises a frequency modulated carrier at a given frequency. The method also includes regenerating the primary illuminator signal. The method also includes canceling the primary illuminator signal from the co-channel interference signals. The method also includes identifying a secondary illuminator signal from a secondary illuminator. The secondary illuminator signal comprises a frequency modulated carrier at the given frequency. The method also includes regenerating the secondary illuminator signal from the co-channel signals.
According to another embodiment, a method for mitigating co-channel interference is disclosed. The method includes canceling a primary illuminator reference signal. The method also includes canceling a secondary illuminator reference signal.
According to another embodiment, a method for mitigating co-channel interference in a bistatic radar receiving co-channel signals comprising target signals reflected by targets and direct signals transmitted by remote transmitters is disclosed. The method includes receiving the co-channel signals at an antenna coupled to the bistatic radar. The method also includes performing adaptive beam forming to obtain a primary illuminator reference signal. The primary illuminator reference signal is from the direct signals and comprises a frequency modulated carrier at a given frequency. The method also includes regenerating the primary illuminator reference signal from the co-channel interference signals. The method also includes performing adaptive beamforming to obtain a secondary illuminator reference signal. The secondary illuminator reference signal is from the direct signals and comprises a frequency modulated carrier at the given frequency. The method also includes regenerating the secondary illuminator reference signal from the co-channel signal from the co-channel signals. The method also includes canceling the secondary illuminator reference signal from the co-channel interference signals.
According to another embodiment, a system for mitigating co-channel interference is disclosed. The system includes an antenna array to receive signals. The system also includes a primary cancellation component to cancel a primary illuminator reference signal from the received signals. The system also includes a secondary cancellation component to cancel a secondary illuminator reference signal from the received signals.
According to another embodiment, a method for detecting targets by a bistatic radar system using transmitted signals and reflected signals from the targets is disclosed. The method also includes converting the received signals into co-channel signals. The method also includes adaptive beamforming a secondary illuminator signal from the co-channel signals. The method also includes regenerating the secondary illuminator signal. The method also includes canceling the secondary illuminator signal from the co-channel signals and mitigating co-channel interference.
According to another embodiment, a method for mitigating interference in a bistatic radar that receives direct path signals and target path signals transmitted as commercial broadcast signals from remote transmitters is disclosed. The target path signals are reflected off targets such that the target path signals have a doppler shift with reference to the direct path signals. The method includes identifying a secondary illuminator signal within the direct path signals. The method also includes cancelling the secondary illuminator signal from the received signals.
According to another embodiment, a method for mitigating interference in a bistatic radar that receives direct path signals and target path signals transmitted as commercial broadcast signals from remote transmitters is disclosed. The target path signals are reflected off targets such that the target path signals have a doppler shift with reference to the direct path signals. The method includes identifying a secondary illuminator signal within the direct path signals. The method also includes canceling the secondary illuminator signal from the received signals.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or maybe learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.